In a radio communication system, a terminal is required to establish a connection with a network, which is generally referred to as a random access procedure. In a long term evolution (abbreviated as “LTE”) system, the random access procedure is generally required to be performed in the following situations: the terminal initially accessing to establish a radio link (transformed a radio resource control (abbreviated as “RRC”) state from an idle state (RRC_IDLE) to a connected state (RRC_CONNECTED)); re-establishing a link after the radio link is interrupted; the terminal establishing an uplink synchronization with a target cell in a switching process; in the case that the terminal is in the RRC_CONNECTED state and the terminal does not established the uplink synchronization, establishing the uplink synchronization when uplink data or downlink data is received; a user located based on an uplink measurement; performing a scheduling request in the case where no special scheduling request resource is assigned on a physical uplink control channel (abbreviated as “PUCCH”).
There is a contention based random access procedure and a non-contention based random access procedure in the LTE. The contention based random access procedure generally includes: randomly selecting, by a user equipment (abbreviated as “UE”), a random access preamble sequence from a RAP sequence set; sending the selected random access preamble sequence on a random access resource (a physical random access channel (abbreviated as “PRACH”)) predetermined by a base station (eNodeB, abbreviated as “eNB”); receiving a random access response (abbreviated as “RAR”) message issued by the base station, on a physical downlink shared channel (abbreviated as “PDSCH”); transmitting, by the UE, a random access procedure message to the base station on a physical uplink shared channel (abbreviated as “PUSCH”) determined based on the RAR message according to a cell-radio network temporary identity (abbreviated as “C-RNTI”) in the RAR message, where the random access procedure message includes an identifier of the UE located in this cell and is used for a contention resolution; and receiving, by the UE, a contention resolution message sent by the base station. In this way, the random access procedure may be implemented.
The non-contention based random access procedure includes: sending, by the UE, the random access preamble sequence predetermined by the base station, on the random access resources predetermined by the base station; and determining, by the UE, that the random access successes when the RAR message corresponding to the preamble sequence transmitted by the UE is received.
In 3rd generation partnership project (abbreviated as “3GPP”), four types of coordinated multi-point transmission (abbreviated as “CoMP”) scenes are provided. In one scene, all transmission points share one cell identity (ID) in a macro region which includes a macro site and a radio remote head (abbreviated as “RRH”). This architecture is also referred to as a distribute antenna system (abbreviated as “DAS”).
In the DAS system, in one cell, the base station only feeds back one RAR with respect to the identical PRACH preamble sequence identity detected on the same PRACH time frequency resource. Thus, the probability of the same random access preamble sequence selected by different UEs increases, as the number of the UEs increases. Therefore, the collision probability is increased during the transmission of the RAR and the success rate of the random access is reduced.